1. Field
The present disclosure relates to a control apparatus for an automatic transmission.
2. Description of the Related Art
Known conventional multi-stage automatic transmissions have a planetary gear mechanism. Such an automatic transmission disclosed, for example, in Japanese Unexamined Patent Application Publication No. 2005-273768 is able to make gear change to any of eight forward gear stages by using a first planetary gear mechanism for input, second and third two planetary gear mechanisms for gear change, and six engagement mechanisms including friction clutches and brakes.
In the above-mentioned automatic transmission, increase in a rotational difference between friction members of any of the engagement mechanisms with respect to the input rotation with a predetermined gear change stage selected may cause an excessive work loss of the engagement mechanism. Consequently, reduction in the acceleration of a vehicle and/or an increase in the temperature of hydraulic oil in the automatic transmission may occur.
On the other hand, in a multi-stage automatic transmission, for the sake of improvement of the fuel efficiency and driving performance (drivability) of the vehicle, it is necessary to increase the flexibility of shifting to a gear change stage by achieving quick and smooth operation allowing not only gear change to an adjacent gear change stage, but also skip gear change with one stage or two stages skipped. For this purpose, by achieving a skip gear change using only, for example, engagement shift between two of a plurality of engagement mechanisms, quick and smooth gear change operation may be implemented and variation of shifting between gear change stages may be increased.
In Japanese Patent No. 2775951 describes a conventional technology related to the above-described rotational difference of an engagement mechanism. The automatic transmission described in Japanese Patent No. 2775951 has multiple engagement combinations in pattern as engagement combinations of engagement mechanisms for achieving a predetermined gear change stage. When gear change is made to a target gear change stage from the predetermined gear change stage for an engagement combination pattern in which a rotational difference of a rotational member increases, the engagement combination is changed to another engagement combination pattern in which a rotational difference of a rotational member decreases, and then gear change is made to the target gear change stage.